When using a React-Query mutation, I have a component that displays an error message. but Typescript doesn't recognize the mutation.error property as type Error:
if (mutation.isError){
console.log(mutation.error.message); // Property 'message' does not exist on type 'unknown'.
console.log((mutation.error as Error).message); // works
}
How can I inform typescript that mutation.error is indeed an Error object?
You’d have to provide the generics to useMutation:
useMutation<MyData, Error>
But I wouldn’t do that. Errors are unknown because at runtime, also non-error objects can be thrown.
I think the easiest solution is to perform an instanceof check instead of checking for isError:
if (mutation.error instanceof Error){
console.log(mutation.error.message);
}
This will correctly narrow the type of error so that .message is available
